Window coverings such as venetian blinds are well known in which a so-called headrail or channel supports a horizontal shaft. The horizontal shaft carries the tapes or cords on which the slats of the venetian blind are supported. Rotation of the rod in one direction or the other will tilt the slats one way or the other, thus closing and opening the blind.
Operation of the control rod may be through a pulley and continuous chain, or may be by means of a worm and wheel, and a wand rotating the worm, so as to thereby rotate the shaft.
The shaft on which the tapes or cords are wound, can only be rotated a certain distance in either direction, and will then stop. If, however, excessive torque is applied to the shaft, the blind can be damaged.
Accordingly, it is desirable to incorporate a torque limiting device so that if the continuous chain or wand is rotated beyond the point at which the shaft must stop, the chain or wand will simply rotate, and the torque limiting device will prevent the rotation being transmitted to the shaft. Various different types of clutch devices have been proposed, in most cases being of considerable degrees of complexity requiring costly tooling, and time-consuming assembly. In addition, as the design of venetian blinds becomes further and further refined, the space available for incorporating such a torque limiting device becomes more and more restricted.
In window coverings in many case a worm and gear wheel drive is used, axis of the wheel in the mechanism is offset with respect to the axis of the shaft. As a result, it is also necessary to incorporate some form of flexible coupling, to take into account the lack of alignment, and this further complicates the incorporation of a torque-limiting device.
However, in one case a flexible drive was used having a drive shaft coupling secured to one end, and a gear coupling at the other end, which did incorporate a form of torque limiting device, but it was relatively expensive.
In some window covering assemblies, a rotatable shaft is provided in the headrail for raising and lowering the drapes or blind slats. In such assemblies, it is also desirable to provide a transmission or clutch mechanism for limiting rotation of such shaft beyond certain limiting positions.
This invention provides a transmission mechanism for use in window covering assemblies of the type including a headrail having disposed therein a control shaft on rotation of which the positions of the drapes or blind slats may be adjusted and in which the transmission mechanism is operative to limit rotation of such a shaft while preventing accidental damage to the drive or transmission mechanisms if a person operates the drive mechanism in an attempt to move the shaft beyond such limiting positions.
This invention provides a novel coupling for use in such a transmission mechanism.
This invention also provides a novel form of bearing for supporting the shaft in the headrail.
One design of such venetian blind assemblies is shown in U.S. Pat. No. 4,531,563.
The design disclosed in this patent involves the use of a headrail of channel shaped construction, having two edge flanges. The tilt rod was supported on two or more bearing assemblies. Each of the bearing assemblies consisted of generally U-shaped rectangular metal components which could be snap fitted in the headrail and secured in position by frictional engagement with edge flanges on the headrail.
In this design, however, it was necessary to provide additional rod retention components also of a generally inverted U-shaped sheet metal construction, which could be snap fitted into the headrail after the insertion of the tilt rod in the bearing assemblies, and then retaining the tilt rod in position in the bearing assemblies.
Thus each of the bearing assemblies consisted of two separate components. Each of the components had to be snap fitted into the blind headrail at separate times, requiring two distinct operations for the completion of each bearing assembly.
In addition, since the components illustrated in that patent were formed of sheet metal, their construction was relatively expensive. As a result that design, while having met with considerable commercial success in the past, is nevertheless relatively expensive in terms of the actual components themselves and is also relatively costly in terms of the abandoned required for assembly.
In addition to these features of this earlier design, the tilt rod itself was retained at one end in a tilt control drive mechanism, of a type which is generally well known in the-art, although different designs are provided by different manufacturers.
However, in order to retain the tilt rod in position in engagement with the drive assembly, it was necessary in this earlier design to provide a form of stop mechanism engaging the free end of the tilt rod remote from the gear drive, to retain the one end of the tilt rod in engagement with the tilt drive. This meant that yet another component again formed of sheet metal, had to be designed and manufactured and supplied and then assembled in order to provide a complete functional blind.
A further design of tilt rod bearing for venetian blinds is illustrated in U.S. Pat. No. 4,333,510. In that form of bearing, the bearing assembly consisted of a one piece integral moulded structure. The structure incorporated two U-shaped bearings for the tilt rod. One of the U-shaped structures incorporation abutments to retain the tilt rod in position.
In that form of structure, the bearing assembly had lower leg portions adapted to extend through the lower central web of the headrail, and had tooth formations engaging either side of an opening in the lower web portion of the headrail.
In that form of bearing, openings were provided in the lower portion of the bearing structure for passage of the tilt elements and the suspension elements but without the provision of any antifriction bearing. As a result, extensive use would cause wear on the plastic around the openings.
A still further form of blind assembly is illustrated generally in U.S. Pat. No. 4,945,970 issued Aug. 7, 1990 entitled CORD LOCK UNIT FOR DRAPE OR BLIND ASSEMBLY.
However, no details of the bearing assembly are illustrated in that patent.
It is, therefore, apparent that it is desirable to provide such a venetian blind assembly in which the tilt rod is supported in bearings of integral one piece moulded construction, which bearings both support the tilt rod and also retain it in the headrail, and in which the bearings are securely held relative to the headrail against movement, and in which the bearing assemblies incorporate antifriction means for passage of the flexible tilt elements and flexible support element.
Other objects of the invention will become apparent as the description herein proceeds.